Selig has said no fewer than seven times in the past 16 months that this was his plan, so the news doesn't exactly come as a surprise. But the formal nature of it is a first—it seems that, this time, he really means it. (Unlike when he said he would retire in 2009, but didn't, and when he said he'd step down in 2012, but again didn't.)

Baseball has had more ups than downs during Selig's tenure. Revenues have grown sharply, attendance is up, and the game is as popular as ever. Even if national TV ratings are down, local viewership has exploded, with many teams scoring their own cable channels in their markets, a practice begun when the New York Yankees created the YES network in 2002.

Selig also oversaw the creation of the wild-card playoff format in 1995 and then the second wild card last year. He also began interleague play, which fans seem to love, and instituted instant-replay usage in certain situations.

Perhaps his most important achievement, though, is the extended period of peace between the players and owners, following the disastrous strike in 1994. Since then, the NBA and NHL have seen work stoppages, and the NFL came a hair's breadth away from missing the start of the 2011 season.

Along with those successes, though, there is the performance-enhancing-drug saga, which continues to this day (see: Biogenesis). People have begun referring to the period of exploding offensive numbers from 1995-2004 as the "steroid era," a phrase that will likely be used as frequently as "Selig era" when people discuss the last 20 or so years of baseball. Selig did finally address PEDs vigorously starting in 2004 with testing and has worked with the players union since then to install harsh penalties for failed tests.

Here is the statement Selig released through MLB's public relations department:

It remains my great privilege to serve the game I have loved throughout my life. Baseball is the greatest game ever invented, and I look forward to continuing its extraordinary growth and addressing several significant issues during the remainder of my term.

I am grateful to the owners throughout Major League Baseball for their unwavering support and for allowing me to lead this great institution. I thank our players, who give me unlimited enthusiasm about the future of our game. Together we have taken this sport to new heights and have positioned our national pastime to thrive for generations to come. Most of all, I would like to thank our fans, who are the heart and soul of our game.